**4.** *Metarhizium rileyi*

*Metarhizium rileyi* (Farlow) Kepler S.A. Rehner & Humber (Ascomycota: Clavicipitaceae), formerly known as *Nomuraea rileyi* (Farlow) Samson, is a potential agent for microbial control of insect pests that can cause considerable agricultural productivity loss [72]. *M. rileyi* was firstly described as *Botrytis rileyi* in 1883, then as *Spicaria rileyi* (Charles 1936) and later moved to the genus *Nomuraea* (Kish, Samson, and Allen 1974). In 2014, Kepler, Humber, Bischoff, and Rehner transferred the fungi to the genus *Metarhizium*. It is an entomopathogenic fungus commonly known to infect and cause mortality in insects, particularly the lepidopterans [73–75]. The spores of this fungus penetrate the body of the host through the cuticle or by ingestion when the larvae are feeding. This fungus grows inside the larvae and

*Role of Microbial Biopesticides as an Alternative to Insecticides in Integrated Pest Management… DOI: http://dx.doi.org/10.5772/intechopen.100400*


#### **Table 3.**

*Summary of some studies on the control of cotton pests by using* Metarhizium rileyi*.*

reproduces, resulting in internal tissue destruction. The fungus is host-specific and eco-friendly, making it significant in integrated pest management [76]. However, *M. rileyi* has been rarely developed and commercialized [77]. As a result, the host range of *M. rileyi* has been reported to be only around 60 species compared to fungi such as *B. bassiana* [74]. Under favourable environmental conditions, caterpillars from the Noctuidae family are mostly attacked by this pathogen [78].

This fungus is a biological control agent for about 30 species of orders Lepidoptera [79], although two species of order Coleoptera are also found to be susceptible [80]. As a well-known entomopathogenic fungus used in the biological control of pests, limitations such as the long pathogenic process and its application are limited [81]. On the contrary, Jaronski and Mascarin [82] have claimed that *M. rileyi* can be easily produced than other fungi. *M. rileyi* has been broadly studied, mainly on its efficacy against cotton bollworm *H. armigera* [83–85]. **Table 3** presents some research work on the control of cotton pests using *M. rileyi*.

#### **5. Nucleopolyhedrovirus**

Baculoviruses belong to the family Baculoviridae, which consists of four genera, including Alphabaculovirus [94]. Viruses from this family have been recorded since 1911, and their natural hosts include almost 700 insect species, mainly belonging to the orders Lepidoptera, Hymenoptera, and Diptera [95]. Baculoviruses are insectspecific [96, 97] and are usually limited to one or a few insect species [98, 99].

Because of their specificity, these viruses can form part of the resistance management strategy [100], demonstrating genetic variations among species [98].

Several members of baculoviruses that display promising results have been successfully developed into commercial biopesticides to control agricultural and forest insect pests worldwide [101]. However, the application of these pesticides has a limited acceptance due to marketing, slow speed of kill, and difficulties with registration and mass production [102]. The production relies mainly on baculoviruses infection and transmission in vulnerable hosts as well as harvesting and purification [103]. Although viruses can be an alternative to synthetic insecticides, they depend on integrating other management strategies [104]. Baculoviruses are part of integrated pest management programmes to control pests in field crops [102]. Despite the regular use of baculoviruses as biopesticides, biological insecticides based on the bacterium *B. thuringiensis* remain the most used biopesticides [94].

Nucleopolyhedrovirus (NPV) is a naturally occurring pathogen that belongs to the group of Alphabaculovirus, and it is a lepidopteran-specific virus [105]. The virus reproduces in the host cells, causing nuclear polyhedrosis disease, and the outbreak of the virus may assist in controlling the host population [106]. The nucleopolyhedrovirus has the potential to control the target insects without harming the environment, pest predators, and parasitoids [107]. *Helicoverpa armigera* nucleopolyhedrovirus (HearNPV) is specifically developed to control *H. armigera,* and the formulations are commercially available throughout the world [108]. The first commercialization of HearNPV was done in China in 1993 [106]. It is reported to have significant potential as a biopesticide in the field [102, 109]. Nucleopolyhedrovirus can be used in conjunction with other insecticides to control


#### **Table 4.**

*Summary of some studies on the control of cotton pests using nucleopolyhedrovirus.*

*Role of Microbial Biopesticides as an Alternative to Insecticides in Integrated Pest Management… DOI: http://dx.doi.org/10.5772/intechopen.100400*

*H. armigera* [110, 111]. It is recommended that the application of HearNPV must commence when cotton starts flowering, and the pests are observed in the field [108]. However, the interaction between HearNPV and host insects remains poorly understood [112]. Bolldex™ is one of the commercial labels currently registered as a HearNPV to control *H. armigera* [102]. Below (**Table 4**) is a summary of some studies on the efficacy of the nucleopolyhedrovirus against cotton pests.
